The present invention relates to the deflection yoke for use in a color cathode-ray tube in which three electron guns are provided in an in-line arrangement, particularly the side pin-cushionless self-convergence type deflection yoke through which three electron beams can be correctly converged all over the screen only with the deflection magnetic field generated by the deflection yoke.
Generally in case of a color television set which is provided a color cathode-ray tube in which three electron guns are in-line arranged, the deflection yoke for deflecting three electron beams is adapted to comprise a horizontal deflection coil which is formed so that the horizontal deflection magnetic field is of a pincushion type and a vertical deflection coil which is formed so that the vertical deflection magnetic field is a barrel type, whereby a proper picture is obtained only by the deflection field or the convergence device is simplified by producing such deflection magnetic field.
However, in the vertical deflection magnetic field as described above, a pincushion type distortion takes place at both horizontal end sides of the picture and becomes a large distortion due to a combination with the pincushion type distortion which results from the curvature of the fluorescent screen of the cathode-ray tube.
As a method to eliminate such pincushion type distortion, that is, the side pin-cushion distortion, the vertical deflection coil is wound so that the vertical deflection magnetic field generated from the vertical deflection coil is formed as a pincushion type at the screen side, that is, the front side of the deflection yoke and as a barrel type at the electron gun side, that is, the rear side of the deflection yoke. The deflection yoke of this construction is referred to as the side pincushionless self-convergence type deflection yoke.
For generation of the above-mentioned vertical deflection magnetic field, the vertical deflection coil which is to be toroidally wound around the annular core should be made as the V-shaped toroidal coil by concentratedly arranging the conductor in a narrow area at the screen side dividedly winding the conductor at two positions of the electron gun side as described in the U.S. Pat. No. 4,246,560.
In case of this method of winding, the conductor is wound with a constant tension applied during winding work and therefore the conductor slips at the edge of the core, thus unabling to position a number of turns of winding at the specified position of the edges of the core. In some cases, for this reason, the shape of the core is deformed as described in said U.S. patent but it is difficult to manufacture this type of core and obtain high dimensioned accuracy of the core and furthermore the deformation of the core brings about an unnecessary deformation of deflection magnetic field. As another example for materializing the above-mentioned winding method, a winding guide frame which is provided with a number of grooves in its periphery is fitted to the front edge and the rear edge of the core, respectively, to avoid slipping of the conductor as described in the U.S. Pat. No. 3,711,802. However, though this example of the core is extremely effective for positioning the conductor if the number of turns of winding is few, the V-shaped winding is undesirable due to a disorder of the winding turns resulting from that the conductors to be wound in a certain specified groove cannot be accommodated in that groove.
It is considered for eliminating such defect to deepen the grooves on the winding guide frame. While the grooves are provided in the plane passing through the core axis, the winding is wound around the core in the plane which does not pass the core axis, and therefore the conductor is obstructed by a wall between the grooves, and accordingly the winding cannot be effectively wound and a sufficient winding angle cannot be ensured, thus deteriorating the efficiency of winding work. Moreover, a bending stress is caused on the wall which forms the grooves by the tension applied to the winding during winding work and may break the wall.
The core which is provided with the vertical deflection coil as described above is mounted on the coil separator as in case of the conventional. If the deflection coil is toroidally wound in the V-shape, the turns of winding are convexed due to a small diameter of the core at the electron gun side, and accurate positioning and fixing of the core in reference to the coil separator cannot therefore be carried out.